1. Field of the Invention
The present invention relates to a bridging device and a method and a program product for controlling the bridging device, and in particular, it relates to a bridging device that relays data transmitted from a router to a communication terminal and a method and a program product for controlling the bridging device.
2. Description of the Related Art
Internet Protocol version 6 (IPv6) has come into widespread use in recent years as a protocol for communication between terminals via networks.
In IPv6 communication networks, a router on a network transmits a router advertisement (RA) packet containing identifying information of the router and a network prefix to a communication terminal on the network. The communication terminal that has received the RA packet generates its own global unicast address using the network prefix contained in the received RA packet. The communication terminal communicates with a communication terminal on another network via the router that has sent the RA packet using the generated global unicast address (for example, refer to Narten, T., E. Nordmark, and W. A. Simpson, “Neighbor Discovery for IP version 6 (IPv6), RFC2461, December, 1998”).
The RA packet sent from the router includes, in addition to the above-mentioned router identifying information and network prefix, information on the valid period (lifetime) for insuring the validity of the information. The router sends RA packets at regular intervals to update the lifetime. However, the router identifying information and the network prefix contained in the RA packet do not change unless the router is replaced with a new router or the network prefix is changed to a different value. Accordingly, in networks in which the replacement of the router or the change of the network prefix hardly occur, the communication terminal continues receiving RA packets only for updating the lifetime at regular intervals.
It is not desirable that a communication terminal continues receiving RA packets only for updating the lifetime of the router identifying information and the network prefix at regular intervals because it increases the load of packet processing on the communication terminal. Particularly, the increase in load due to the continuous reception of RA packets is undesirable to low-cost communication apparatus with a low processing capability because it results in a decrease in the data processing capacity of the sensor node.
Furthermore, when a plurality of routers is present on the network, the communication terminal must receive RA packets that are regularly sent from the routers. This may cause a significant decrease in the throughput of the communication terminal.
If RA packets are frequently sent from a router to a communication terminal on a network, the transmission efficiency of the network may be decreased.
The IPv6 communication of the related art thus has the problem of increasing the load on a communication terminal because it receives RA packets from a router at regular intervals.